Traveling wave tube with heat pipe cooling

ABSTRACT

A method and apparatus for efficiently removing heat from a traveling wave tube. A copper barrel heat sink casing is concentrically disposed about an inner glass or quartz tube with an annular space therebetween. Hollow ceramic spheres fill the space between the tube and the heat sink, and a small amount of fluid, such as a fluorocarbon serves as a vaporization agent to aid in the dissipation of the heat generated within the inner glass or quartz tube.

Umted States Patent 1 1 1111 3,749,962 Smith et a1. 1 51 July 31, 1973 [54] TRAVELING WAVE TUBE WITII IIEAT PIPE 3,405,299 10/1968 Hall et a1. 313/19 X COOLING 2,993,682 7/1961 111m; 165/104 x 2,958,021 10/1965 Comelison et a1.... 165/104 M 1 Inventors: Sidney Smith; Lester Winslow, 3,667,542 6/1972 Parkes 165/104 both of Alexandria, Va. 3,524,497 7/1970 Chu et a1. 165/104 X Assignee: The Unied States of America a 3,344,306 9/1967 Levm 313/18 X r gf igg g g gs SDecetary of the Primary Examiner--Rudo1ph V. Rolinec D Assistant 'gqgrniner-Saxfieldflhannon, Jr. 1 Fllcdl 1972 I Att0rneyR. S. Sciascia, Arthur L. Branning et al. 211 Appi. No.2 237,676 I p [57] ABSTRACT 52 US. Cl 315/35, 313/18, 165/105, A method and apparatus for efiicienfly removing heat 1 5/135 g g 37g 219 274 from a traveling wave tube. A copper barrel heat sink [5 1 Int. Cl. 1101 25/34 casing is concentrically disposed about imlcr glass [58] Field of Search 313/18, 19; 219/274, quartz tube with an annular Space thflrebetwfien- 219 3 5 373; 1 5 0 1 104 05 135 3 low ceramic spheres fill the space between the tube and 315/15 the heat sink, and a small amount of fluid, such as a fluorocarbon serves as a vaporization agent to aid in the [56] References Cit d dissipation of the heat generated within the inner glass UNITED STATES PATENTS quam tube- 3,444,419 5/1969 Hansen et a1. 315/35 5 Claims, ZDrawing Figures 1 l4 I l I I I I r I 1 I I I I I PATENIED JUL3 l TRAVELING WAVE TUBE WITH HEAT PIPE COOLING BACKGROUND OF THE INVENTION and have comprised a helical conductor enveloped in a quartz or a glass casing. The outside of the. quartz or glass structure is subjected to a particular cooling system so as to dissipate the high heat generated within the tempts to efficiently dissipate this high heat without suffering a substantial RF loss.

One of the most common techniques for dissipation of the heat, especially for higher powered systems, is to support the helix within a vacuum envelope by means of three or more dielectric rods spaced equally around the helix and parallel to its axis and in contact with both the envelope and the helix. This arrangement provides both mechanical support for and alignment of the helix within the envelope and a thermal path therebetween. The wide use of this technique attests to its general acceptance by the industry. However, this acceptance is qualified by some severe performance limitations. One limitation is the low heat dissipation capability of this arrangement. The area of contact between the support rods and the helix is very small thus limiting the heat conduction between the helix and the rod at a low rate. Attempts at increasing the area of contact and substituting material having a higher thermal conductivity have been of limited success because of the adverse effects on the electrical characteristics of the tube.

A second and very significant problem arising from the rod support technique is the increased dielectric loading and lowered interaction impedance. Microwave dielectric loading due to the presence of the dielectric rods disposed alongside the helix decreases the efficiency and gain of the tube and decreases its operating bandwidth. Many attempts atreducing theldielecv tric loading have been made, usually resulting in a compromise configuration which would provide acceptable heat conduction through the dielectric supports while trying to maintain a low dielectric loading.

Another technique for cooling the helix attempted in the prior art is to form the helix of metal tubing and pump a fluid coolant throughout the length of the helix.

' helical, slow wave structure. There have been many atthe helix and is collected at the exit end by a collector v the inner glass or quartz helix tube is therefore efficientlytransmitted to a concentrically disposed copper heat sinkz' i g i" OBJECTS OF THE INVENTION It is therefore an object of the present invention to; provide an efficient radial cooling means for a pipe or 1 similar annular structure.

Another object of the invention is to provide cooling means for a helix or other microwave traveling wave tube.

pipe cooling means without adding RF loss or dielectric loading.

Other objects of the invention will be readily apparent to those skilled in the art by referring to the follow ing detailed description in connection with the accompanying drawing wherein:

THE DRAWING FIG. 1 is a cross-sectional view of the device for effciently removing heat from the traveling wave tube;

and

FIG. 2 is an end view of the structure shown in FIG. A

concentrically disposed around traveling wave tube 13. The essence of this device is to transmit the heat gener ated with traveling wave tube 13 to a heat sink such as the copper cylinder 18 without adding RF loss or dielectric loading.

The heat which is to be removed from the tube 13 is a result of electromagnetic radiation propagated through the tube. Specifically, radiowave energy is introduced into the helix at an inlet microwave coupling (not shown). A beam of electrons from an electron gun (not shown) is directed axially through the middle of anode (not shown). The electromagnetic wave traveling along the helix 12 is amplified by interaction with an electron beam traveling down the axis of the helix.

It is this interaction which is responsible for generating the heat from tube 13.

The heat generated by the radio frequency losses in the helix and impingement of the electron beam during this interaction is removed from tube 13 in the following manner:

The simplicity of the technique is appealing but in practice it has not worked well because the tubing must be very fine, and as a result the pressure drop of the fluid in the tube is prohibitively and dangerously high.

As can be easily seen, an effective method of efficiently removing heat from a traveling wave tube without displaying the drawbacks set forth above has not been available.

SUMMARY OF THE INVENTION The space between the traveling wave tube and the metal cylindrical heat sink is filled with chunks or particles of a metamorphic material such as ceramic spheres I 16. The selection of a particular material substantially depends upon the maximum acceptable dielectric constant permitted. We have found that hollow ce- I I ramic spheres having a diameter of approximately 1 millimeter, such as those manufactured by Emerson and Cummings Corp., work exceptionally well. In any event, the metamorphic material is filled into the space j .3

between the two annular members while they are held by a jig in their correct positions. Although the spheres should not be ,packed or forced into the space, there should be enough spheres so that the space is completely filled when the lateral axis of the device is parallel to the ground.

A further object of the invention is to provide a heat The hollow ceramic spheres 16 are suspended in a small amount of the liquid coolant, and the space between the annular members are sealed so as to provide a closed system. The sealing should take place in a vacuum to remove the majority of the air present in the tube. Although many types of liquid coolant are satisfactory, it is important that the fluid have insulative properties and preferably a low dielectric constant. Also, the coolant should have a boiling point of approximately 100 to 300 C as well as a high heat of vaporization. We have found that a fluorocarbon, which as a low RF loss, such as FC-45 or FC-75 made by 3-M Corporation, works well.

The heat generated in the tube 13 is transferred to the fluorocarbon-ceramic sphere medium and the fluorocarbon is vaporized and tends to migrate toward the outer heat sink. The heat of the fluorocarbon is dissipated by the heat sink 18 and as a result the vapor is reduced to a liquid upon removal of the heat. The ceramic spheres serve as a wick and are responsible for providing a returning surface for the fluorocarbon. That is'to say, the ceramic spheres permit the fluorocarbon to return toward the glass tube, so the heat dissipation cycle can begin again.

Obviously many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed and desired to be secured by letters patent of the United States is:

, 1. A device for transmitting heat away from a heated 4 pipe structure comprising:

heat sink means enclosing at least a portion of the length of the pipe structure such that a space exists between said pipe structure and said heat sink means;

pieces of metamorphic material creating a wicking action disposed in said space;

liquid means partially filling said space;

whereby the heat from the structure vaporizes the liquid, said sink absorbs said heat, and said liquid returns toward said structure by way of the pieces of metamorphic material.

2. The device as claimed in claim 1 wherein said metamorphic material is hollow-ceramic spheres.

3. The device as claimed in claim 1 wherein said pipe structure is a traveling wave tube.

4. The device as claimed in claim 1 wherein said liquid means is a fluorocarbon.

5. A device for transmitting heat away from a helical traveling wave tube comprising:

a copper barrel heat sink enclosing the tube such that an annular space exists between said tube and said heat sink;

hollow ceramic spheres creating a wicking action disposed in said space; Y

fluorocarbon material partially filling said space;

whereby the heat from the structure vaporizes the fluorocarbon, said copper barrel heat sink absorbs said heat and said fluorocarbon reduces to the liquid state, and returns toward said tube by way of the ceramic spheres.

i Il t i 

1. A device for transmitting heat away from a heated pipe structure comprising: heat sink means enclosing at least a portion of the length of the pipe structure such that a space exists between said pipe structure and said heat sink means; pieces of metamorphic material creating a wicking action disposed in said space; liquid means partially filling said space; whereby the heat from the structure vaporizes the liquid, said sink absorbs said heat, and said liquid returns toward said structure by way of the pieces of metamorphic material.
 2. The device as claimed in claim 1 wherein said metamorphic material is hollow ceramic spheres.
 3. The device as claimed in claim 1 wherein said pipe structure is a traveling wave tube.
 4. The device as claimed in claim 1 wherein said liquid means is a fluorocarbon.
 5. A device for transmitting heat away from a helical traveling wave tube comprising: a copper barrel heat sink enclosing the tube such that an annular space exists between said tube and said heat sink; hollow ceramic spheres creating a wicking action disposed in said space; fluorocarbon material partially filling said space; whereby the heat from the structure vaporizes the fluorocarbon, said copper barrel heat sink absorbs said heat and said fluorocarbon reduces to the liquid state, and returns toward said tube by way of the ceramic spheres. 